Determinants of unwitnessed out-of-hospital cardiac arrest: a systematic review (HL-D-26-00618).

In 30 seconds

This systematic review synthesized observational studies of demographic, socioeconomic, clinical, and situational factors associated with witnessed status among adults with out-of-hospital cardiac arrest (OHCA). Across 22 studies involving 210,028 individuals, female sex and arrest occurring at home were the factors most consistently associated with unwitnessed OHCA. Evidence also suggested associations with several other characteristics and circumstances, but was limited and predominantly based on unadjusted analyses. The review’s findings may inform targeted prevention and public health strategies, although they do not establish that these factors cause arrests to go unwitnessed.

Key findings

• The review included 22 observational studies with 210,028 individuals.
• Female sex and arrest occurring at home were most consistently associated with unwitnessed OHCA.
• Limited, predominantly unadjusted evidence suggested higher unwitnessed-arrest rates among Black individuals and people with low socioeconomic status or greater area deprivation.
• Type I diabetes, psychiatric illness, nighttime or sleep-related arrests, and residential or rural settings were also suggested as associated factors.

Why it matters

Unwitnessed OHCA is associated with very low survival, and identifying circumstances linked to unwitnessed events may help shape prevention and public health efforts. The review highlights home arrests and female sex as the most consistent associations, while also showing that evidence for other factors is limited. These findings can help frame further research into recognition and prevention without implying causation.

What to keep in mind

The evidence came from observational studies, and findings for several determinants were based predominantly on unadjusted analyses; associations do not establish causation.